Abstract

Following their birth in olfactory placode, luteinizing hormone-releasing hormone (LHRH)-containing neurons migrate across the developing cribriform plate and form a dispersed population in the mammalian basal forebrain. The present study reveals the colocalization of unique glycoconjugate antigens (detected with monoclonal antibody CC2) on a subset of LHRH-immunoreactive (LHRHir) cell bodies and growth cones in the rostral forebrain during embryonic development in rats. In addition, LHRHir neurons were found along CC2-immunoreactive (CC2ir) fibers in the nasal cavity, across the cribriform plate, and in the rostral forebrain. At embryonic Day 16 (E16) approximately 20% of the LHRHir neuronal population in the forebrain had the CC2 epitope on surfaces of cell bodies. This percentage fell as the number of LHRHir neurons in the forebrain increased. Prior to the detection of LHRH-containing neurons, beginning on E14, CC2ir glycoconjugates were observed on vomeronasal cells and axons and also on a dorsomedial subset of olfactory neurons and axons. As early as E14 CC2ir fibers extended into the rostral forebrain. LHRHir neurons were seen in close apposition to CC2ir fibers in both the nasal cavity and rostral forebrain. These studies raise the possibility that CC2ir glycoconjugates provide a specific chemical guide for a subset of LHRH neurons along a part of their migratory pathways. The small percentage of LHRHir neurons which have CC2ir on their surfaces prenatally may constitute a selective homogenous functional subgroup within the population of LHRH neurons.